The key to accurate ammunition is concentricity and uniformity in every respect. Cartridge cases received directly from a manufacturer typically bear non-uniformities and eccentricities from piece to piece that can affect the potential accuracy of the ammunition. Competitive marksmen usually rework each cartridge case in order to produce ammunition with greater concentricity and uniformity and hence the potential for improved accuracy.
A typical prior art cartridge case 10 is shown in FIG. 7. A bullet (not shown) is held in place by the cartridge neck 14 (terminating in a mouth 15) of the cartridge case 10. An extractor groove 19 circumscribes the cartridge case 10 near its bottom. A primer pocket 18 contains a primer, which ignites when struck by the firing pin of the gun being used. A flash hole 20 connects the primer pocket 18 with the propellant chamber 22, so that the ignited primer will ignite the propellant contained in chamber 22 thereby forcing the bullet (not shown) out of the neck 14.
Among the non-uniformities typically present from one cartridge case 10 to another cartridge case 10 is the size and shape of the flash hole 20, which is sometimes partially occluded by burrs extending from the inner perimeter of the flash hole 20. Even a small difference between flash holes 20 can affect the ignition, chamber pressure, and velocity uniformity, which in turn affect the uniformity and accuracy of the ammunition. Moreover, any non-uniformity between primer pockets 18 will affect the propellant ignition uniformity by altering the contact of the primer with the bottom of the primer pocket, thereby changing the firmness of primer seating and the firing pin-to-primer relationship, which in turn affects ignition characteristics and ammunition uniformity.
Non-uniformities in the form of wall thickness variations at the neck 14 and the mouth 15 of the cartridge case also affect the neck/bullet/rifle chamber concentricity, bullet alignment in the bore of the firearm, and accuracy of the ammunition. Any variation in the thickness of different portions of the circumference of the neck may cause the bullet to be held in misalignment with a firearm""s bore, forcing the bullet into an imperfect shape under chamber pressure when fired. Non-uniformities and eccentricities of this type from cartridge case to cartridge case cause accuracy to deteriorate.
In a first separate aspect, the present invention comprises a device for machining a cartridge case that has a neck comprising a circular neck wall, a mouth and a primer pocket. The device comprises a gripping assembly, adapted to accept and retain a cartridge case and a neck machining assembly, positioned to engage the cartridge case from a first direction and adapted to machine the neck of the cartridge case. Additionally, a primer pocket machining assembly is positioned to engage the cartridge case from a second direction, opposed to the first direction, thereby permitting simultaneous primer pocket and neck engagement, and adapted to machine the primer pocket.
In a second separate aspect, the present invention is a device for machining a cartridge case that has a neck, a mouth and a primer pocket. The device comprises a gripping assembly, adapted to accept and retain a cartridge case and a neck machining assembly, adapted to machine the neck of the cartridge case. In addition, a mouth machining assembly has a fixed positional relationship to the neck machining assembly so that the mouth machining assembly engages and machines the mouth of the cartridge simultaneously to the machining of the neck of the cartridge case by the neck machining assembly.
The foregoing and other objectives, features and advantages of the invention will be more readily understood upon consideration of the following detailed description of the invention, taken in conjunction with the accompanying drawings.